| 1. |
- Ervasti, Esa, et al.
(författare)
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Behaviour of longitudinal surface cracks in the hot rolling of steel slabs
- 1999
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Ingår i: Journal of Materials Processing Technology. - 0924-0136. ; 94:2-3, s. 141-150
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour of a longitudinal V-shaped crack, on the surface of a continuously cast steel slab, is studied during hot rolling. The analysis is carried out by means of the commercial FE-code LS-DYNA3D. Process parameters obtained from industry are used as a reference. The slab of initial width 1000 mm and thickness 220 mm is rolled down to 30 mm. It is assumed that the material can be treated as rigid-perfectly plastic and that the cracks do not propagate. The latter assumption is in agreement with industrial observations for a steel grade similar to that analysed here. The aim of the study is to investigate the possibility of controlling the plastic deformation so that the cracks disappear or so that their deteriorating effects are minimised. The analysis is focused upon the influence of friction, roll radius and rolling schedule on the change in the shape of a crack of initial depth 20 mm and a crack angle of 6 degrees. The reliability of the simulations is checked by pilot-plant experiments using aluminium as the model material for steel.The results indicate that it is not possible to prevent the bottom side surfaces of the crack from coming into contact, especially not for small reductions/pass and small roll radii. The influence of friction was found to be marginal. Contact between the crack surfaces is found already at the beginning of the rolling, as the V-shaped crack is being changed to Y-shape. Considering the upper part of the crack, this remained open during the majority of the schedules studied. However for heavy reduction/pass and a large roll radius, this part of the crack is closed also, but not before the final passes. If the bottom side surfaces of the crack are in complete contact, they are prevented from further oxidisation. It is assumed that for such conditions the deteriorating influence of the bottom part of the defect decreases during subsequent rolling. During the elongation of the workpiece, the oxide flake of the Y-crack bottom is broken into splinters with oxide free material in between, making the creation of a high performance weld possible. Provided that this supposition is correct, the best results should be obtained for Light reductions/pass at the beginning of the rolling, resulting in an early closure of the crack bottom, followed by heavy reductions/pass enabling also the closure and oxide splintering of the upper part of the folded crack.
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| 2. |
- Ervasti, Esa, et al.
(författare)
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Transversal cracks and their behaviour in the hot rolling of steel slabs
- 2000
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Ingår i: Journal of Materials Processing Technology. - 0924-0136. ; 101:1-3, s. 312-321
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour of transversal cracks in reverse rolling of steel slabs is analysed. For this purpose a commercial FE-program, LS-Dyna3D has been utilised. Process parameters from an industrial rolling mill have been used as a reference. One basic assumption is that the cracks do nor propagate for the steel considered. This is in agreement with observations in industry. Furthermore the material is treated as elastic-plastic. The aim of the study is to investigate the possibility of controlling the plastic deformation so that the cracks disappear at the same time as their boundary surfaces are prevented from getting into contact with each other. If they should get into contract, a defect in the form of an oxide flake should be created. The optimum situations are assumed to be found when the depth of the crack decreases more rapidly than the height of the slab at the same time as the crack width increases. For such rolling conditions it should be possible to find the crack bottom on the workpiece surface without any trace let by the original crack.During rolling two phenomena are present, counteracting each other. At the entrance to the roll gap, the crack widens, which is regarded as beneficial. The explanation to the phenomenon is that when the front edge of the crack gets into contact with the roil it is dragged towards the gap at the same time as its velocity is rapidly changed from horizontal to become parallel to the tangential velocity of the roll. If this phenomenon did not occur, the risk for the creation of a permanent oxide Rake should be big. During the passage of the gap the widened crack angle is decreased. The decrease of the angle is explained by the high hydrostatic pressure that is associated with the roll/workpiece contact surface. At the exit the angle is slightly increased once again which might be explained by the fact that the back edge of the crack is still in contact with the roll and its movement is retarded because of friction. Thus the final result depends on which of the two phenomena, widening or contraction that has been dominating.The analysis shows that light reductions/pass, small roll radius and high friction are preferred. A deep crack of V-shape is easily transformed to Y-shape. This means that a remaining defect should be formed at the bottom of the crack. Reverse rolling is found to be beneficial because this way of rolling implies that the crack does nor tilt so easily which should result in the formation of an oxide flake.
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| 3. |
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| 4. |
- Nilsson, Anders, et al.
(författare)
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Zinc-alloys as tool materials in short-run sheet-metal forming processes - Experimental analysis of three different zinc-alloys
- 2002
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Ingår i: Journal of Materials Processing Technology. - Elsevier. - 0924-0136. ; 125-126, s. 806-813
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, there has been an increasing demand from manufacturing industries for new tool materials such as more wear resistant zinc-alloys, with optimised characteristics regarding short-run sheet-metal parts production. Research on zinc-alloys wear resistance has been performed by a lot of research groups. However, it is very difficult to compare the wear resistance of these materials due to the fact that the investigations have been carried out with conventional methods, such as pin-on-disc or block-on-ring tests. In this paper wear resistance has been evaluated for three different zinc-alloys with different primary phase as die-tool material in forming process equipment. The method used has been the U-bending process, in which the conditions are realistic due to the complex varying load and strain during the forming process. The primary phase in ACuZinc5 is a F-phase, which is harder and stronger than the primary phases in Norzak2 and ZA27. ACuZinc5 is almost nine times more abrasive resistant and Norzak2 is 1.8 times more abrasive resistant than ZA27. An other conclusion that can be drawn is the importance of using a methodology during the experimental work that has realistic conditions, both for the tool material and sheet-metal.
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| 5. |
- Skåre, T, et al.
(författare)
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Monitoring of friction processes by the means of acoustic emission measurements—deep drawing of sheet metal
- 1998
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Ingår i: Journal of Materials Processing Technology. - Elsevier Science SA. - 0924-0136. ; 80-81, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic emission generated in deep drawing processes gives information about the friction and the forming processes between tool and workpiece. This information can be used to supervise or improve the forming process. Measurements of acoustic emission in manufacturing machines in production lines shows that different events such as, galling, tool wear, lubricating failure, different viscosity of lubricants, stick-slip, necking and cracking of the sheet metal can be separated in time- and frequency domain. Laboratory tests show that proportionality exists between the effective output of the friction surfaces and the measured effective output of the AE-sensor in drawing a sheet metal between flat dies. The measured acoustic emission has been influenced by the smoothness, lubricants, relative speeds between the friction surfaces, the contact pressure between the surfaces, galling, changed geometry's of friction surfaces and different types of material in contact. In a forming process will different lubricants result in different lubricity and the measured effective output of the AE-sensor result in a ranking method. The proportionality between the effective output of the friction surfaces and the measured effective output of the AE-sensor established in the laboratory tests has been applied in measurements of acoustic emission in manufacturing machines in production lines. By monitoring the acoustic emission in manufacturing machines, we are able to detect different events, i.e. galling, cracks, toolwear.
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| 6. |
- Walter, M F, et al.
(författare)
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Machining of ring shaped worn pieces
- 1995
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Ingår i: Journal of Materials Processing Technology. - Elsevier Science B.V.. - 0924-0136. ; 48:1-4, s. 239-245
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Tidskriftsartikel (refereegranskat)abstract
- The connection between the tolerances possible to obtain in a machining process and the machining forces and clamping forces in turning of ring-shaped work pieces clamped in conventional chucks with varying jaw numbers has been investigated. The results can be used for adaptive control of the clamping forces in an optimal way so that the work piece does not come loose in the course of machining and the desired tolerances can be obtained.
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| 7. |
- Zhou, Jinming, et al.
(författare)
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A system for monitoring cutting tool spontaneous failure based on the cutting edge stress estimation
- 1995
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Ingår i: Journal of Materials Processing Technology. - Elsevier Science B.V. - 0924-0136. ; 48:1-4, s. 231-237
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Tidskriftsartikel (refereegranskat)abstract
- Cutting tool spontaneous failure such as, edge fracture and chipping are common phenomena in the metal cutting process, especially when difficult workpiece materials which have poor cutibility are met in the machining process. The tool failures are often caused by high mechanical and thermal stresses acting in it. Monitoring stresses acting in a cutting edge during machining process can provide more reliable means to monitor and to predict tool spontaneous failure. In this paper, The design and implementation of a real time monitoring system has been introduced intending to monitor the spontaneous failure of a cutting tool in a turning process. The system is based on a VME computer system and a real time kernel. The system includes a high speed data acquisition subsystem and a graphic presentation subsystem. The strategy for monitoring is based on the estimation of stresses acting in a cutting tool. On-line stress estimations are obtained according to in-process measured cutting forces, load functions and cutting parameters and cutting tool geometry.
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| 8. |
- Edberg, Jonas, et al.
(författare)
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Wedge rolling test
- 1994
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Ingår i: Journal of Materials Processing Technology. - Elsevier S.A.. - 0924-0136. ; 42:2
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- A method for the evaluation of friction models is described. A wedge is rolled to uniform thickness, a range of reductions being investigated thereby in one experiment. Finite-element simulations are performed in order to estimate the friction parameters that can be used in the simulation of hot rolling. The influence of the material parameters and the friction parameters on the calculated results are investigated and the latter are compared with experimental results. It is shown that it is possible to separate the influence of the material parameters and the friction parameters, thus enabling the friction parameters to be evaluated from a minimum number of experiments.
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| 9. |
- Hansson, Lars, et al.
(författare)
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The effect of microwave drying on Norway spruce woods strength: a comparison with conventional drying
- 2003
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Ingår i: Journal of Materials Processing Technology. - Elsevier S.A.. - 0924-0136. ; 141:1
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- The purpose of the present work was to investigate whether the drying method itself affects strength of wood apart from fibre direction, density, temperature in the wood, moisture content and with which angle the microfibril is placed in the middle layer at the secondary cell wall S2. The drying methods compared were microwave drying and conventional air-circulation drying, and the species tested was Norway spruce. The result shows that it is not possible to demonstrate any difference between the two drying methods with respect to the strength of the wood. What affects wood strength are such variables as moisture content, number of annual rings and the density properties weight, width and thickness
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| 10. |
- Ivarson, Anders, et al.
(författare)
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Oxidation dynamics of laser cutting of mild steel and the generation of striations on the cut edge
- 1994
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Ingår i: Journal of Materials Processing Technology. - Elsevier S.A.. - 0924-0136. ; 40:3-4
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- Over the past two decades CO2 laser cutting has grown from an obscure laboratory technique into an important branch of manufacturing engineering. The most commonly cut materials are steels and a great deal of industrial and scientific research has been carried out on the laser-material interactions that generate a cut. This paper concentrates on the phenomena which give rise to a cyclic cutting event when a CO2 laser in conjunction with an oxygen jet is used to cut mild steel. The nature of the cut edge striation produced by the cyclic oxidation reaction is explained thoroughly and a possible oxidation cycle is postulated. It is demonstrated that the key to understanding the cyclic nature of the cutting event is the self-limiting nature of the oxidation of the steel in the cut zone
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